These are the englyns that were sung at the Cad Goddeu (the Battle of the Trees), or, as others call it, the Battle of Achren which was on account of a white roebuck and a welp; and they came from Hell, and Amathaon ab Don brought them. And therefore Amathaon ab Don, and Arawn, King of Annwn (Hell), fought. And there was a man in that battle, unless his name were known he could not be overcome; and there was on the other side a woman called Achren, and unless her name were known her party could not be overcome. And Gwydion ab Don guessed the name of the man, and sang the two Englyns following:

"Sure-hoofed is my steed impelled by the spur;
The high sprigs of alder are on thy shield;
Bran art thou called, of the glittering branches."

And thus,

"Sure-hoofed is my steed in the day of battle:
The high sprigs of alder are on thy hand:
Bran by the branch thou bearest
Has Amathaon the good prevailed."

From Pen 98b, 81-2.
Translated from the Myvyrian Archaeology by Lady Charlotte Guest, in her notes on the
Mabinogion.